I'm trying to understand why can't I get the same results in LTSpice as in my calculator.

For this signal

V_out=12sin(314t) [V]

I want to know what's V_out for t=3S

With my calculator (in rad) I guet V_out = 0V if I use 2*pi*50*3 as the sin argument and I get V_out = -5.518V if I use 314*3 as sin argument and with LTSpice, using measure command I get 0.0387292V...

Check your calculator value.
At time t=3 sec there will have been an integral number of 50Hz AC cycles. So the value of the sine function at that instant must be zero.

Click to expand...

I've checked it with my calculator... In rad mode, if I use 12sin(2*pi*50*3) it returns zero but if I use 12sin(314*3) it returns a non sense value. Looks like in rad mode, pi as an specific meaning for the calculator!

I was expecing to get the same result because 2*3.14*50*3 is equal to 314*3...

I've checked it with my calculator... In rad mode, if I use 12sin(2*pi*50*3) it returns zero but if I use 12sin(314*3) it returns a non sense value. Looks like in rad mode, pi as an specific meaning for the calculator!

I was expecing to get the same result because 2*3.14*50*3 is equal to 314*3...

When you do a TRAN analysis in LTSpice (or any other version of Spice) and have a sinusoidal voltage or current source, you specify the peak amplitude; so for 12 Vrms you would then use 16.97 volts, as you indicated.

On the other hand, if you're doing an AC analysis, all that matters is that you use the same interpretation (i.e., rms, peak, peak-to-peak, etc.) throughout.